• 한국전자파학회논문지
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• 제26권8호
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• pp.758-764
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• 2015

본 논문에서는 2차 함수 곡선의 회전체형 도체 곡면 위에 있는 컨포멀 배열 안테나의 패턴을 EAGA(Enhanced Adaptive Genetic Algorithm)를 이용하여 합성한 내용을 보이고 있다. 다양한 곡면의 회전체 도체를 고찰하기 위해 2차 함수의 계수를 바꿔 세 가지 유형의 회전체형 곡면을 형성시켰고, 각 유형의 컨포멀 배열 안테나 패턴을 합성하였다. 패턴 합성에 소요되는 시간의 단축을 위해 3차원 컨포멀 배열 안테나의 능동 소자 패턴 대신에 2차원 평면 배열 안테나의 능동 소자 패턴을 구한 후, 이를 오일러 변환(Euler transform)시켜 이용하였다. EAGA를 이용하여 합성된 패턴의 검증을 위해 MWS(Microwave Studio)를 통해 구한 패턴과 비교하였으며, 두 패턴은 전반적으로 유사하였다.

• Advanced Composite Materials
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• 제18권1호
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• pp.1-20
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• 2009

This paper describes the results of experiments and numerical simulation studies on the impact and indentation damage created by low-velocity impact subjected onto honeycomb sandwich panels for application to the BIMODAL tram. The test panels were subjected to low-velocity impact loading using an instrumented testing machine at six energy levels. Contact force histories as a function of time were evaluated and compared. The extent of the damage and depth of the permanent indentation was measured quantitatively using a 3-dimensional scanner. An explicit finite element analysis based on LS-DYNA3D was focused on the introduction of a material damage model and numerical simulation of low-velocity impact responses on honeycomb sandwich panels. Extensive material testing was conducted to determine the input parameters for the metallic and composite face-sheet materials and the effective equivalent damage model for the orthotropic honeycomb core material. Good agreement was obtained between numerical and experimental results; in particular, the numerical simulation was able to predict impact damage area and the depth of indentation of honeycomb sandwich composite panels created by the impact loading.

• 소성∙가공
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• 제29권1호
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• pp.20-26
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• 2020

In the design of the metal forming processes, various types of ductile fracture criteria are used to predict crack initiation and to fabricate metallic products without any defects. However, the quantitative measurement method for determination of crack initiation is insufficient. It is very difficult to detect crack initiation in ductile metals with excellent deformability because no significant load drop is observed due to crack generation. In this study, the applicability of acoustic emission sensors, which are commonly used in facility diagnostics, to measure crack initiation during the metal forming process was analyzed. Cylindrical notch specimens were designed using the finite element method to induce a premature crack on the surface of pre heat-treated steel (ESW90) material. In addition, specimens with various notch angles and heights were prepared and compression tests were carried out. During the compression tests, acoustic emission signal on the dies and images of the surface of the notch specimen were recorded using an optical camera in real time. The experimental results revealed that the acoustic emission sensor can be used to detect crack initiation in ductile metals due to severe plastic deformation.

• 한국산학기술학회논문지
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• 제6권6호
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• pp.536-541
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• 2005

고무 성분에 대한 대변형 및 강성은 비선형 및 대변형의 해석 결과로 나타낼 수 있다. 또한 고무는 Mooney-Rivlin의 모델로서 적용되고 고무들 사이에서 자기 접촉이 성립되어지는데 강성체 및 고무 사이에서는 마찰력이 있게 된다. 본 연구에서 사용된 비선형 시뮬레이션 해석은 여러 가지의 고무 성분들의 설계, 분석 그리고 개발에 널리 사용될 수 있다. 이러한 방법을 이용하면 새로운 고무 제품을 개발하는데 있어서 시간과 비용을 절감할 수 있을 것으로 보인다. 고무 성분들의 분석은 특이한 재료의 모델링과 비선형 유한 요소 해석을 요하는데 금속 부품들에 대하여 해석하는 프로그램들과는 완전히 다르다. 본 연구의 목적은 대변형 및 비선형의 고무 부품을 해석하는데 있다.

• Advances in Computational Design
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• 제2권4호
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• pp.333-348
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• 2017

Inspections of ancient metallic bridges have illustrated fatigue cracking in riveted connections. This paper presents a comparison between two alternative finite element (FE) models proposed to predict the fatigue strength of a single shear and single rivet connection. The first model is based on solid finite elements as well as on contact elements, to simulate contact between the components of the connection. The second model is built using shell finite elements in order to model the plates of the riveted connection. Fatigue life predictions are carried out for the shear splice, integrating both crack initiation and crack propagation lives, resulting from the two alternative FE models. Global fatigue results, taking into account several clamping stresses on rivet, are compared with available experimental results. Proposed comparisons between predictions and experimental data illustrated that the proposed two-stage model yields consistent results.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 1997년도 춘계학술대회 논문집
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• pp.552-556
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• 1997

The Direct Metal Prototyping(DMP), one of the rapid prototyping technologies, allows the manufacturing of three-dimensional metallic parts using metal powders directly from the CAD data. Laser power and scanning speed are the most important variables of the process. The objective of this study is to obtain the design data for laser power and scanning speed to bond metal powders effectively using the finite element method. To obtain the design values, a numerical analysis considering two-dimensional heat transfer during the sintering of metal powder layers of the process was performed. The laser beam has been modeled to have directionality in its heat flux distribution, i. e., in the scanning direction a Gaussian beam mode distribution has been assumed and in the thickness direction a square beam mode distribution. The three-dimensional irregular distribution of metal powders of the powder layer is idealized as two-dimensional distribution in which metal powders are located regularly and periodically on the plate. In this study the design values of laser power vs scanning speed have been obtained. Temperature distribution and temperature variation of the powder layers with respect to time have been predicted. The commputed dsign data will be useful in determining the initial conditions of the process.

• 열처리공학회지
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• 제9권2호
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• pp.147-158
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• 1996

Generally, analytical consideration on the behaviour of metallic structures during quenching process, and analysis on the thermal stress and deformation after heat treatment are very important in presumption of crack and distorsion of quenched material. In this study a set of constitute equations relevant to the analysis of thermo elasto-viscoplastic materials with strain hysteresis during quenching process way presented on the basis of contimuum thermo-dynamics mechanics. The thermal stresses were numerically calculated by finite element technique of weighted residual method and the principle of virtual work. In the calculation process, the temperature depandency of physical and mechaniclal properties of the material in consideration. On the distribution of elasto-viscoplastic thermal stresses according to radial direction, axial and tangential stress are tensile stress(50MPa, 1.5GPa and 300MPa) in surface and compressive stress(-1.2GPa, -1.14GPa and -750MPa) in the inner part on the other hand, radial stress is tensile stress(900MPa) in area of analysis. According to axial direction, tangential stress gradients are average 60MPa/mm on the whole. The reversion of stress takes place at 11.5 to 16.8mm from the center in area of analysing.

• 한국대기환경학회지
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• 제15권3호
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• pp.291-303
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• 1999

The purpose of this experimental study is to investigate seasonal deposition flux variations of the total dustfall and various inorganic elements in it. Total of 84 dustfall samples were collected from September, 1997 thur August, 1998 at 7 different sites in Kunsan. Each sample was analyzed by an AAS to determine the levels of 5 inorganic elements Zn, Cd, Cr, Fe and Pb. Deposition fluxes, soluble/total fractions for each element were extensively investigated. Estimated depositon fluxes of dustfall and elements in Kunsan were in the range of 37.5~45.1 ton/$ extrm{km}^2$/yr for dustfall, 43.5~81.8kg/$\textrm{km}^2$/yr for Zn, 6.6~11.0kg/$\textrm{km}^2$/yr for Cd, 44.8~110.0kg/$\textrm{km}^2$/yr for Cr, 223~323 kg/$\textrm{km}^2$/yr for Fe, 10.9~22.3 kg/$\textrm{km}^2$/yr for Pb, respectively. Thus, the estimated average total deposition fluxes of dustfall in Kunsan(376.35$\textrm{km}^2$) per day were 43.3 ton and 58.6 kg for Zn, 8.9 kg for Cd, 80.6 kg for Cr, 293.8 kg for Fe and 14.1 kg for Pb, respectively.

• 소성∙가공
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• 제21권8호
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• pp.499-505
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• 2012

The fuel cell is a very promising power generation system combining the benefits of extremely low emissions, high efficiency, ease of maintenance and durability. In order to promote the commercialization of fuel cells, a flexible forming process, in which a hyper-elastic rubber is adopted as a medium to transmit forming pressure, is suggested as an efficient and cost effective manufacturing method for fuel cell bipolar plates. In this study, the ability of this flexible forming process to produce the micro channel arrays on metallic bipolar plates was first demonstrated experimentally. Then, a finite element (FE) model was built and validated through comparisons between simulated and experimental results. The effects of key process parameters on the forming performance such as applied load and punch velocity were investigated. As a result, appropriate process parameter values allowing high dimensional accuracy without failure were suggested.

• 수산해양기술연구
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• 제53권3호
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• pp.302-307
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• 2017

An electric steam boiler equipped with a condensate recovery system, which stores the condensate generated after using steam in steam washers, steam cookers, steam irons, and steam cleaners in a condensate tank and supplies compressed air to the condensate tank so that the condensate is recovered to the boiler by the pressure of the compressed air, was studied. In the results of this study, the heat energy balance between the quantity of the heat generated by the non-metallic surface heating element and the quantity of the heat absorbed by the water was good in a range of ${\pm}5%$. In addition, the heat transfer rate increased in proportion to the electric power of the surface heating element heater, the waste heat energy was normally recovered by the recovery of the condensate of the steam boiler equipped with the high compression waste heat recovery system, and the recovery rate of the waste heat exhibited 23%.